An increase in tremors deep under California’s San Andreas fault may be the harbinger of a major earthquake, according to a study out Friday in the journal Science. Seismologist Robert Nadeau of the University of California at Berkeley reached this conclusion after analyzing tremors along a segment of the San Andreas Fault near Parkfield, California. Nadeau found that after the 2003 6.5-magnitude San Simeon quake and the 2004 6.0-magnitude Parkfield quake — both located mid-way between San Francisco and Los Angeles — tremors became more frequent and underground stress increased at the end of a “locked segment” of the San Andreas fault.
